1. Field of the Invention
This invention relates to top drive well drilling, operations, apparatuses, equipment and particularly to improved input driving power, improved pipe handling systems, improved pipe wrenching means, improved dolly roller system and improved support means for pipe elevator links.
2. Description of the Prior Art
It has previously been common in well drilling and other well operations to impart motive force to the drill string or other tubular members by means of the old rotary table drive apparatuses or by electric motor top drives. The old rotary drive tables are inefficient and costly. The electric top drives have had numerous problems; for example, to move and support drill strings weighing up to 500 tons, the direct current traction motors used in electric top drives must be very large, consequently they require a large and effective motor cooling system. Also all of the safety problems associated with electricity are considerations when using an electric top drive. Because of these shortcomings, obtaining compliance with accepted safety codes and insurance certification for the use of electric top drives has been a tedious, expensive, and time-consuming process. There are also numerous structural/functional disadvantages associated with the use of electric top drives; for example, some prior art electric top drive utilizes an expensive thrust bearing to support the drill string rather than using the shaft of the motor itself. Other prior art electric top drives have an electric motor which is offset from the shaft supporting the drill string The central drive shaft of the electric motor is not directly connectable to the drill string nor is it directly connectable via an intermediate sub or other member. Therefore, a means for transferring rotative force from the electric motor to the drill string must be employed; e.g. a system of reduction gears between the motor and a tubular member which is connectable to the string. This results in an imbalance in the distribution of the reactive torque applied to the string.
One type of top drilling drive previously utilized includes pipe handling mechanism suspended below and connected to the top drive gear box (see U.S. Pat. No. 4,449,596). This top drive also utilizes a pipe wrenching device supported in suspension from the gear box and both its pipe handling mechanism and the pipe wrenching device are permanently disposed about the tubular drive shaft projecting from the bottom of the top drive. In actual operation, the pipe wrenching device is actuated upwardly to engage splines located about the circumference of the tubular drive shaft. When drill rotation is stopped, the pipe wrenching device can be used to break a threaded connection between the powered drive unit and the drill string, and the pipe handling mechanism can then support the drill string remaining in the drill hole. This top drilling drive utilizes an electric motor to impart the necessary rotary motion to the drill string. Utilities, cables, and other connections to the top drive to the electric motor must of necessity be flexible since they must travel up and down with the top drive.
The previously described top drilling drive assembly has had a number of operational disadvantages. When providing power to the drive motor, rubber covered flexible conductors are provided. These conductors are largely unprotected from accidental short circuits which might occur if the cable were pinched between two metal objects Since all drilling rigs are located in hazardous areas this could be life threatening. The electric motor must also be cooled and the cooling air is transported through flexible ducts which are very prone to failure if they are of a flimsy nature. The motors must be completely sealed to prevent the emission of sparks from the carbon brushes. This has proved to be very unreliable. Another disadvantage has been the pipe wrenching device. This tool requires hydraulic fluid conductors directed to the working mechanism. Since in operation, the top drive shaft which supports the wrenching device, must rotate, this demands that a high pressure rotary fluid connection must be provided on the top drive shaft. This is very costly and unreliable. Such a large diameter rotary joint at higher pressures is not reliable. Remotely operated shut-off valves have failed. These valves all utilize a ball with a hole through the center through which passes abrasive drilling fluids. The present valves do not provide a satisfactory method of ensuring the ball is fully open or closed. When the ball is not oriented properly, fluid passage will erode the ball very quickly.
The drill pipe pick up tool requires tilting the top drive central shaft about its vertical axis to pick up a new section of pipe. With this method it is impossible to pick up a length of drill pipe without exerting extreme pressure on the side of the pipe. This results in undue wear on the drill pipe and also the "mouse hole." (A "mouse hole" is a hole near the rig in which pipe is placed for pick up).
Other operational disadvantages of the top drive of U.S. Pat. Nos. 449,596 and 3,766,991 include the fixed rollers on the "dolly." This fixture secures all the other top drive components to the derrick guide rail system. Since there is no flexibility in the dolly roller system to compensate for irregularities, many roller failures have been experienced in the field. It has been difficult to obtain certification for use of electric top drives in hazardous areas. Because of the electrical and the cooling system requirements, several safety devices in the form of electrical switches must be provided. Individual components require certifications and the entire installation must be approved by a recognized authority. This is very time consuming and expensive. The prior art hydraulic top drives such as taught in U.S. Pat. No. 3,994,350 has a hydraulic motor which is offset from the centerline resulting in an imbalance of loading of the central shaft. An endless chain is driven by the hydraulic motor and the chain, in turn, drives a drive unit which can be threadedly connected to pipe.